The present invention relates generally to 14-karat gold alloy compositions, and, more particularly, to improved 14-karat gold alloy compositions having enhanced yellow color, reversible hardness, and a fine grain structure.
It is well known that gold, a precious metal, is relatively soft. To this end, it has been known to alloy gold with other elements and compounds in an attempt to improve its hardness and other properties. The amount or quantity of gold in such alloys is commonly expressed in terms of a karat weight. A composition having 100% gold is known as a 24-karat composition. However, if the alloy has a lesser amount of gold, this is commonly expressed in terms of a particular karat weight, which is a percentage of the amount of gold. For example, a 14-karat alloy would have 14/24=58.33% gold, with the balance being other elements and/or compounds.
The present invention relates generally to 14-karat gold alloy compositions that are used in the manufacturing of jewelry. It has been known to form alloys based on a gold-silver-copper-zinc system. The usage and application of these various alloys are typically defined by their main physical properties, such as hardness, strength, elongation, melting temperature range, grain size, color, and the like. These properties can be measured, and are often incorporated in the specifications of the alloy.
As noted in U.S. Pat. No. 6,406,568, the color of gold alloy compositions is no longer a matter of subjective impression. Rather, a color is now determined objectively in terms of its component colors, a* (green-red) and b* (blue-yellow) on a CieLab color-measuring system. This method of measuring color is described in G. Raykhtsaum et al., xe2x80x9cThe Color of Goldxe2x80x9d, A. J. M. (October 1994). While color is now measured objectively, the consumer appeal of a particular color or tint is still subjective.
Some gold alloys have been developed that offer the capability of reversibility, by selective application of an appropriate heat treatment, between their annealed-hardness and aged-hardness values. In many cases, there is a considerable difference between these hardness values. Hence, an alloy may be annealed to lower its hardness value. This allows the alloy to be worked more easily. After the alloy has been worked, and the article thereof formed or repaired, the article may be aged-hardened to a higher hardness value to increase its resistance to denting and deformation. However, if there is a subsequent need to rework or repair the item, it may be annealed to reduce its hardness back down to its annealed-hardness value. After the item has been reworked or repaired, it may be aged-hardened to increase its hardness to a higher hardness value. Some gold alloys having this xe2x80x9creversiblexe2x80x9d hardness feature are shown and described in U.S. Pat. Nos. 5,180,551 and 6,406,568.
Grain structure is another characteristic that materially affects the value of an alloy. It has been known to add iridium, cobalt and/or nickel to produce an alloy having a fine grain structure. However, the use of these additives have to be closely controlled for fear of separation of these elements or formation of xe2x80x9chard spotsxe2x80x9d in the alloy. Nickel is a known cause of an allergic reaction with the skin that results in dermatitis. The use of these various grain refiners is discussed in Ott, xe2x80x9cOptimizing Gold Alloys for the Manufacturing Processxe2x80x9d, Gold Technology, Issue No. 34 (Spring 2002) [at pp. 37-44].
Other gold alloy compositions are shown and described in U.S. Pat. Nos. 5,173,132 and 5,749,979. The aforesaid articles and each of the aforesaid patents are hereby incorporated by reference.
Accordingly, the present invention relates generally to improved 14-karat gold alloy compositions that have a desirable yellow color, reversible hardness, and a fine grain structure.
The present invention relates generally to various 14-karat gold alloy compositions having a desirable yellow color, and reversible hardness between their annealed- and aged-hardness values. In some cases, the compositions have a highly desirable fine grain structure, which facilities their use in the manufacture of various items of jewelry.
The improved gold alloy compositions broadly include: about 58.65 weight percent gold; about 11.5-25.0 weight percent silver; about 11.85-23.35 weight percent copper; and about 2.0-7.0 weight percent zinc; wherein the color of the composition has a value of between about xe2x88x923.0 to about 0.5 CieLab a* color units, and a value of between about +20.0 to about +22.0 CieLab b* color units; wherein the ratio of the amount of copper to the amount of silver is between about 0.4-2.0; and wherein the ratio of the amount of copper to the amount of silver plus twice the amount of zinc is less than about 1.0.
The improved composition may further include a grain refiner selected from the group consisting of iridium, cobalt, platinum and iron. The grain refiner may include about 0.2-0.5 weight percent cobalt, 0.1-0.3 weight percent platinum and/or about 0.1-0.3 weight percent iron. In one particularly preferred form, the improved alloy composition has a grain refiner that includes about 0.2 weight percent cobalt, about 0.1 weight percent platinum and about 0.1 weight percent iron. The color of this particular alloy has a value of about xe2x88x921.1 CieLab a* units and has a value of about +22.0 CieLab b* units, a ratio of the amount of copper to the amount of silver of about 0.6, and a ratio of the amount of copper to the amount of silver plus twice the amount of zinc of about 0.48.
In a second particularly-desirable composition, the color of the composition has a value of about xe2x88x920.9 CieLab a* units, and has a value of about +21.0 CieLab b* units. In the second preferred desired alloy, the ratio to the amount of copper to the amount of silver is about 2.0, and the ratio of the amount of copper to the amount of silver plus twice the amount of zinc is about 0.94.
The inventive gold alloy compositions have an annealed hardness of at least about 140 VHN after having been heated to about 1150xc2x0 F. for thirty minutes, followed by a water quench. The improved alloys have an aged hardness of at least about 240 VHN after having been heated to about 600xc2x0 F. for about one hour, and thereafter being allowed to cool to room temperature. The hardness of the inventive compositions is reversible between their annealed- and aged-hardness values.
Accordingly, the general object of the invention is to provide various improved 14-karat gold alloys.
Another object is to provide improved 14-karat gold alloy compositions having desirable yellow color and reversible hardness characteristics.
Still another object is to provide improved 14-karat gold alloy compositions having desirable yellow color, reversible hardness and a fine grain structure.